Mobile devices can serve as sensor devices that collect various types of data from wherever and whenever their owners carry them. Applications on these devices may be used to automatically capture data such as environment audio and video indexed by location and time. Discovering and retrieving such data kept in the mobile devices currently require a central server to access and transfer the data to a common remote location. However, if made accessible to a central server or transferred to a remote location the privacy of the user that collected the data may be compromised.